The Horizon System: At the Hubble Horizon
“Where celestial arches grace the foreign stars
Where the sea hangs above an inverted sky
Where rivers run red with the fumes of tar
Where even mighty death may yet still die
So far from home, lies Grand Horizon.“
- Vassal Seleucidis, excerpt from “Invitation to the Great Beyond“ (2218)
System Overview
Content
The Horizon System is a relatively young star system located in the middling regions of the enormous Comatula Nebula. With four stars, two brown dwarfs and twenty-three planets, it is one of the most complex systems known to science. The system is flush with life, ranging from extremophile bacteria in the subsurface oceans of icy moons to filter-feeding giants ballooning through the skies of super-Venuses. As it wanders the galaxy, it is accompanied by the thousand-strong remnant of a once-grand open cluster known as the Horizon Moving Group, itself rife with strange life.
Lifeforms
At some 1.7 billion years old, Horizon is less than 40% the age of our own Solar System. When Earth was the same age, the only life it had was bacterial scum, but Horizon bucks the trend for young systems. Ten of Horizon’s planets and twenty-three of its moons host complex, multicellular ecosystems rivaling or even exceeding Earth’s in diversity and complexity.
It is a mystery how and why life in the Horizon System became complex and diverse so quickly. Except for the hydrocarbon beings of Marrus, all Horizonian life is believed to have evolved from a single bacterium-like ancestor native to the system’s namesake planet, but it is unknown whether that ancestor was a home-grown organism that emerged from nonliving matter in Horizon’s primordial seas or an immigrant carried by asteroids from a far-off star system. Unless the system from which a hypothetical foreign proto-Horizonian originated is found, this question may never be properly answered.
Society
Like very few others in the universe, the Horizon System has the privilege of hosting a naturally evolved intelligent species. The five species of paradise-terns (Alatornis sp.) are arboreal, dromaeosaur-like pseudo-animals native to the sweltering equatorial jungles of the planet Horizon. Though today they are nomadic pastoralists in the canopies of its montane forests, things were very different a million years ago.
From around 1.1 to 0.8 million years before present, the five species of paradise-terns formed a unified, technologically advanced civilization referred to by historians as Old Horizon. Mastery of biotechnology combined with an aggressively expansionistic war culture to form a truly fearsome imperial power that spread across the Gordian Reach. At its peak, vast cities of cellulose and ivory would have sprawled across a hundred thousand worlds, housing untold trillions of people and all sorts of exotic purposed organisms. So thorough were the Empire’s colonization efforts that even today some 30% of all known species across the Reach can trace their ancestry back to Horizon, while their dominion was so far-reaching that most other sapient life in the galaxy still has an instinctual fear response towards Horizonians. Even now, 800,000 years after it fell to ruin, Old Horizon’s fossilized husk remains a monument to lost grandeur.
Though the blood descendants of Old Horizon have abandoned their ancestors’ legacy, another group has come to emulate it in their stead. During the Cerulean Demise, a contingent of historians and xenoarchaeologists discovered its fossilized capital on the lost continent of R’lyeh Insula, sparking vicious conflicts as rival empires raced to claim the technological legacy of the Old Horizonians. As the Demise reached its fever pitch and the mad crusade of the Siderian Ascendancy finally seized the Horizon System in its grasp, those pioneering scientists who discovered it gave themselves over to the hibernating Last Emperor so that their brethren might live.
The new nation that emerged from the Cerulean Demise is a very different beast from its prehistoric predecessor. Though arborescent towers of engineered flesh once again harvest the light of ten thousand suns, they are inhabited not by individuals like you or I but rather bodiless ‘gestalt patterns’ fluttering through the autonomic husks of a thousand species. A new set of Lords born from the broken memories of an undead sovereign stalk the petrified halls of Old Horizon’s palaces while seven immortal Archons carry the memories of their pioneering progenitors to a myriad of new worlds. But as strange as this hive-minded chorus of dreams and desires may be, it is an undeniable success story - few others could claim dominion over the heavens as the Deathless Empire of Horizon can.
The First Sun: Actinophrys, the Ephemeral Radiance
Actinophrys is an F7 main-sequence white star, currently around 2.2 times brighter, 1.3 times larger, and 1.2 times more massive than the Sun. Its brighter burn means that it will live only around half as long as the Sun will, so it is currently about 1/3 of the way through its life. It is a weak flare star, periodically blasting its surroundings with gigantic eruptions that may double its optical luminosity and quadruple its UV and X-ray output.
One might expect to find little of note around such a young and volatile star, but instead a dizzying array of complex life populates the seas, soils, and skies of eight of its planets. Actinophrys’s living worlds represent one of the most biodiverse regions of the known universe, amassing over twenty million known species between the eight of them.
The Interior Semiresonant Series
The Interior Semiresonant Series is a short set of planets, all of which complete their orbits faster than Mercury does. They are a physically diverse group, with a gas giant, a lava world, a Mars-like desert, and an acidic eyeball Earth among them. All of them formed very early on in the system’s history, rapidly migrating inwards from its icy outer reaches within a few million years of Actinophrys’s formation. All are tidally locked, as their close proximity to their star ensures speedy tidal evolution. Beyond these traits, however, they have very little in common with each other.
Members of the Interior Semiresonant Series
-
Journey to a hellish, crimson Jupiter analogue, hailing from the frigid depths of the great beyond but having found its true calling searing beneath a hateful sun. With its intense gravity and immense bulk, it shares its torturous experience with the remainder of the Horizon System as an agent of Actinophrys’s raging flares.
-
Witness a blasted ruin of a world, stricken by celestial fire and seared by volcanic rage. With its vast oceans of lava beneath a torrid, toxic sky, this viridian hell will not know peace until its fiery end in the belly of its dying sun, billions of years to come.
-
Envision a little world caught between giants. Teetering on the edge of gravitational destruction from all sides, only a tangled conspiracy of opposing forces keep it from a catastrophic end. Nevertheless, it is this combination of forces that sustains its life, long after its central fires should have died.
Rhopalura lies in wait, walking on a thousand razor-thin threads.
-
Marvel in the majesty of an enormous celestial jewel, forged in the fires of creation themselves. From scales of ruby and sapphire to pulsing arteries of quicksilver and gold, this acrid, acidic giant pushes the bounds of possibility in planetary physics.
The Acidian Intermediary
This sparse series consists of three worlds dynamically distant from the other members of Actinophrys’s planetary system. Between the three of them, Navanax is a stripped super-Earth very similar to the members of the Resonant Worlds, while Alvinella and Chrysomallon are a binary pair of leftover protoplanets, each one quite similar to Mars. Like the asteroids of the our Solar System, none of these three worlds are believed to be native to the region.
Members of the Acidian Intermediary
-
Intrude upon the beguiling face of a world gone exotic. Stripped of its erstwhile cloak of supercritical steam, this Earth-shaped acid world wheels through the Horizonian heavens. Swinging through months of darkness and unending light, this harsh planet’s red and golden face unseats all who dare to brave its wrath.
-
Dance between the whirling twin orbs of a planetary pair eternally tracing their tortured waltz through the celestial spheres. Accompanied by an entourage of fragments, they tug and rip at each other, splitting open their crusts and revealing great gouts of magmatic flame.
Alvinella and Chrysomallon sing the song of ruin out into the void.
The Resonant Worlds
The Resonant Worlds are the most populous series of the whole Horizon System, with eleven members in total. As its name implies, all the members of this series are in a complex set of mutual mean-motion resonances, which allow their orbits to pack into a space less than 3 times the size of Earth’s orbit around the Sun. Like most resonant chains in planetary systems, they likely formed as a group of co-migrating mini-Neptunes in the cold outer reaches of the system before reaching their present position straddling the habitable zone. The lack of thick hydrogen atmospheres and deep water envelopes today is attributed to the planets’ near-destruction by a very nearby supernova.
Members of the Resonant Worlds
-
Behold a venerable giant, stalwart in its survival for eons. This Neptunian world survived the supernova that brought an end to its kind’s rule over the Horizon System and ushered in the age of the Living Worlds. Largely unchanged for a billion years, it and its entourage of moons stand as a testament to what once was.
Listen, for ancient Chironex speaks its secrets in hushed and dulcet tones.
-
Examine a minor world of endless sands, eroded and disfigured beyond comprehension. Once a verdant, Earth-like paradise, its oceans have dried and its lands have grown barren as Actinophrys has steadily robbed it of its water. Nevertheless, the few lifeforms marooned on this anaemic world eke out a meagre existence in shadowed canyons and lowland oases, their desire to live carrying them through this endless suffering.
The voice of Tonicella has grown weak, but its determined cry has never waned.
-
Explore a world pushed beyond the brink, rendered completely hostile by a brightening sun. As the oceans slowly evaporated and the surface got hotter and hotter, most life fled the deteriorating conditions by taking to the air, while an exotic domain of wholly alien biochemistry moved into the empty lands below.
-
Regard a pair of acidic paradises, teetering at the edge of habitability. Wracked with volcanic activity and covered in natural nuclear reactors, the metallic, acidic oceans gave birth to a strange ecosystem of quartz trees, metallic gastropod-analogues, and radiation-feeding titans.
The harsh wilds of Acidianus and Thermococcus stand ready to challenge all.
-
Mourn the passing of a once-verdant world, laid low by its own children. A sinister secular resonance among this super-Earth’s extensive array of moons has rained heavenly wrath on its inhabitants below, bringing a mass extinction of epic proportions. In the lichen reefs and bacterial forests that emerged in the aftermath of the disaster, a new set of strange creatures is set to conquer this empty planet.
Changxing stands in desolate silence, waiting for someone to peer through.
-
Journey to an unending ocean flaunting chromatic exuberance far in excess of Earth’s comparably meagre seas. These sun-soaked tropical seas have accrued all sorts of odd hitchhikers and hanging-ons, from ancient biological relics of eras long past to sailors and outlaws the galaxy over.
-
Bask in the glory of a natural splendor far removed from the familiar and ordinary. The youthful biosphere of this carbon-choked jungle world thrives in its unusual conditions, sprouting satellite lineages across the galaxy and giving rise to one of the most diverse and ecologically unique communities in the whole of the known universe.
Horizon blazes with the fires of grand ambition, beckoning the worthy to live their dreams.
-
Peruse an icy beauty of a super-Earth, kept on the brink of a deep freeze with the help of oceans doped with poisonous ammonia. Lashed by brutal winter storms and pelted by meteor showers, this dark, chilly tundra is nevertheless a ground for clever biological innovation divorced from the brutal rat race of Horizon.
Cryogenia scoffs at the lesser worlds with their fleeting lives and ever-changing faces.
-
Gaze upon a trio of clouded, frozen worlds. Two Neptunian holdovers from their past heyday dance through the cold void together, a Mars-sized aquarian ice world trailing the pair together. Draped in shades of grey and blue, they provide a demure end to the splendor of the Resonant Worlds.
The Frigid Exterior, or Solaris In-Waiting
Beyond the Resonant Worlds of Actinophrys’s habitable zone is a largely barren region cleared by the immense gravity of the giant super-Jupiter Rhodactis. With a mass over 5 times that of every other one of Actinophrys’s planets combined, this enormous world utterly dominates the outer region of its system. The only other member of this series, Olindias, is a foreign world in a retrograde, high-inclination orbit that keeps far away from its giant inner neighbor. This is the region where most of Actinophrys’s planets are thought to have first formed, but all except Rhodactis have all left for sunnier pastures.
Members of the Frigid Exterior
-
Embrace the gravitational infinity of a failed star. With eleven times the mass of Jupiter crushed into an electron-degenerate mass nearly as dense as gold, this frigid gas giant hosts an entire solar system in miniature. With fifty round moons and innumerable smaller ones, one could spend lifetimes unpacking the numerous enigmas of this behemoth Author.
Rhodactis lords over the Horizon system, inviting a nonexistent challenge to its splendor.
-
Rendezvous with a foreign world, hailing from the now-vanished arrays of Ceratium’s quarter. Finding safe haven from the rapacious hunger of Physalia, this Saturn-like world has accrued its own impressive array of satellites, including a miniature version of Antipathes-Cerianthus. Cloaked in seas of liquid nitrogen, these small worlds are a last stop before the infinity of interstellar space.
The Second and Fourth Suns: Ceratium and Ceratophorus, the Ruinous Pairing
Ceratium and Ceratophorus are a close binary consisting of an F7 white star and a K4 orange dwarf, orbiting each other with a period of slightly over ten days. The pair have a combined luminosity 2.3 times the Sun’s, though Ceratophorus contributes only 7% of this combined output. They are far enough apart that their mutual gravity does not distort their shapes, but they will devour each other in a luminous red nova as Ceratium reaches old age in 5 billion years, destroying the entire Horizon System.
Binaries such as this are no threat to planetary formation, and indeed many other similar pairings like Marañón-Apurímac of Amazonia or Atelecrinus-Zenometra of Cenometra host dozens of worlds. However, Ceratium and Ceratophorus host none. Only a single ‘world’, the low-mass brown dwarf Physalia, graces their presence, having ejected or devoured every other planetary body they may have once had.
Substellar Provision - Physalia, the Miracle Author
The cosmic dance of Ceratium and Ceratophorus is joined by a titan among worlds.
Brown dwarf Physalia is by far the most massive non-stellar body of the Horizon System, packing over twenty times Jupiter’s mass into a slightly smaller sphere. With a looping, retrograde orbit at the edge of the habitable zone, this titanic world is joined in its chaotic journey through the heavens by an entourage of twenty enormous satellites, a whole constellation of strange life wheeling through the cosmic void.
The Third Sun: Palmaria, the Final Survivor
Palmaria is the last of the four stars of the Horizon System, a dim G6 yellow dwarf. Due to its young age, it has only 60% the brightness of the Sun despite having 98% of its mass. Appropriately for its youth, it is a far less stable star. Palmaria experiences an extensive and irregular sunspot cycle that can decrease its luminosity by up to 10% during the deepest minima. The star also occasionally produces giant superflares and coronal mass ejections over 50 times as powerful as the largest observed solar flares, much like its sibling Actinophrys.
Instabilities in its youth caused most of Palmaria’s planets to consolidate into a single object, creating the habitable-zone brown dwarf Praya just as the same instabilities formed Physalia two stars over. However, not every planet of Palmaria met its doom at the hands of this giant; one gas giant and two co-orbiting terrestrial planets remain.
The Marginal Accompaniments
Three planets of Palmaria have survived the formation of Praya. They have practically nothing in common with each other, for one is a primordial gas giant kicked into the very innermost parts of the system while the others are super-Earths that formed from material accumulating in the L4/L5 basins of Praya. Nevertheless, they are the only remnants of a once-abundant planetary system, the remainder of which has amalgamated into the giant they attend.
Members of the Marginal Accompaniments
-
Swing by the last remnant of a once-proud dynasty. This inflated, low-density hot Jupiter is the only independent planet remaining in its system, its erstwhile siblings cast into space at the hands of great Praya. Whipping around its sun once every 20 hours, this blazing world has been torched dry of even the very clouds themselves.
Resomia hides in the glare of searing sunlight.
-
Cast a glance towards a world abandoned, left in ruin on the far shore. This super-Earth would fit in more in the Resonant Worlds of Actinophrys, but has found itself kicked to the orbit of Praya. Trapped by the immense gravity of its host with no hope of escape, their fates have become entwined.
Agalma ekes out a meagre existence beneath the notice of cannibal giants.
-
Bow to the presence of a grand old world. As the third-largest solid body in the Horizon System, this super-Earth is subordinate to none but the immense might of Praya. Though the surface is crushed by gravity twice as strong as Earth’s, its ring-shadowed oceans still swarm with exotic life.
Stephanomia lounges in the center of a spiral abyss.
Substellar Provision - Praya, the Exotics Author
Praya is a brown dwarf at the very lowest end of the mass range, only slightly above the 13 Jupiter-mass limit where large gas balls begin performing limited nuclear fusion. Nevertheless, it dominates the planetary system of Palmaria, its massive gravity confining the other planets to just a few narrow zones of stability. With clouds of sulphur and brilliant auroral displays, this strange giant cuts a brilliant figure in the sparse system of Palmaria.
Praya is accompanied by fifteen planetary-mass satellites between the mass of the Moon and twice Mars. Though not as grand as their equivalents around Physalia, the Prayan Worlds more than make up for it in terms of their sheer physical diversity - from seas of petrol to flesh-eating jungles to vast, glassy deserts, it seems anything may be found in this constellation of living worlds.
